The present invention pertains to largely unsupported combustion of petroleum coke.
Prior attempts to facilitate the use of petroleum coke in combustion applications, summarized herein, have relied principally on furnace configuration, fuel blending and modification of the physical properties of petroleum coke.
Unsupported combustion of petroleum coke has been achieved in the past in down fired boilers (also known as down shot or arch fired) where solid fuel particles are exposed to relatively long residence times in the combustion zone. The combustion of 100% petroleum coke (often referred to as petroleum coke) has been demonstrated and commercially practiced in circulating fluidized bed combustors (CFBC's) at several locations. These were combustion systems that were specifically designed for the low volatile matter in the petroleum coke and result in long retention times supplemented by a recirculating load of bed material consisting of unburned fuel, ash and sorbent material (limestone).
However, since most existing fossil fuel utility boilers are wall-, corner- or turbo (i.e., generally horizontally) fired, the unsupported firing of petroleum coke in horizontal-fired boilers represents a case of greater practical interest. For the purpose of description of the prior art and the present invention the term horizontally refers to the position of the burner at an angle from coincident with a horizontal axis of the furnace up to an angle of 45° to that horizontal axis. In such units, solid fuel particles experience much shorter combustion zone residence times, rendering the stable and complete combustion of petroleum coke without a support fuel much more difficult to achieve. In fact, the unsupported firing of petroleum coke within a horizontally fired utility boiler has never been demonstrated. A common solution that facilitates the use of petroleum coke in horizontally fired pulverized coal boilers is to blend the petroleum coke with a support fuel; the petroleum coke typically comprising less than 50 wt % of the fuel (see references). Minimization of the petroleum coke within the fuel mixture allows for sufficient volatile matter to stabilize the combustion process.
Prior to the present invention the firing of 100% petroleum coke without any support fuel within a horizontally fired heating unit including, but not limited to, steam generators, industrial boilers and the like has never been demonstrated. For some horizontally fired utility boilers, a common solution is to blend the petroleum coke with a support fuel, with petroleum coke typically comprising less than 80% of the fuel. Minimization of the petroleum coke within the fuel allows for sufficient volatile matter to facilitate complete combustion of the fuel.
Another path is to actually alter the physical and/or chemical characteristics of the petroleum coke to facilitate conventional combustion as described by Patentees in U.S. Pat. No. 6,168,709B1. Patentees suggest alterations to the processes that produce petroleum coke in order to obtain a premium fuel grade petroleum coke that is more suitable for firing. However, even when utilizing a premium, fuel-grade petroleum coke, it has been suggested to use support fuel to improve low load flame stability.
None of the solutions mentioned above take full advantage of the current petroleum coke available on the market. The ability to reliably burn standard petroleum coke in existing horizontally-fired steam generator or utility boilers without alteration or addition of a support fuel would represent a much lower cost option with a greater potential for generating abundant and affordable electricity.
U.S. Pat. No. 4,515,095 teaches and claims methods for combustion of coal/water slurries using oxygen enrichment of the primary air used to burn the coal. However Patentees could not combust coal/water slurries where the volatile content of the coal was below 20%.